Many dispensing systems are known which include a container, holding the product to be dispensed, and a dispensing head having a dispensing channel communicating, on the one hand, with the container holding the product to be dispensed and, on the other hand, with the outside; a pumping member enables the user to dispense the product at will.
It is known that, when the container, of any type, consists of a material which is quite rigid, it is necessary for the upper part of the container to be at atmospheric pressure, that is to say in communication with the atmosphere, in order for the dispensing of the product to be able to be carried out, while air uptake by the container takes place; in order to do this, two-valve air-uptake pumps have already been proposed as pumping member.
U.S. Pat. No. 2,815,890 discloses a dispensing assembly in which means are provided for establishing or preventing, at will, air uptake by the container, by virtue of the dispensing head being mounted so as to be rotationally movable with respect to the container. Contact with the air by the product in the container may thus be reduced over time, thus enabling the product in the container to be protected from possible degradation.
However, after dispensing the product, part of the latter remains in the dispensing channel; this part of the product is in contact with air during the air uptake by the dispensing head and during storage; the product may therefore be degraded by oxidation or contaminated by impurities in the air and, during subsequent dispensing, the product dispensed may have lost its intrinsic qualities, or indeed have become harmless.